The present invention relates to an electrophotographic printer utilizing a means for forming an electrostatic latent image corresponding to information to be printed, on an image-bearing member, a means for developing the electrostatic latent image with a magnetic developer containing magnetic toner, a means for transferring the developed image to a recording medium, and a means for heat-fixing the developed image to the recording medium, and more particularly to an electrophotographic printer which has reduced thinness and improved portability.
In a conventional electrophotographic printer, an electrostatic latent image corresponding to a printer output (information to be printed) is generally formed on a cylindrical photosensitive drum, brought into contact with a magnetic brush of a magnetic developer conveyed on a developing roll containing a permanent magnet roll and disposed opposite the photosensitive drum, so that it is developed (visualized as a toner image). The developed image is then transferred onto a recording paper and heat-fixed.
The magnetic developer usable for a magnetic brush method as mentioned above is in many cases a two-component developer consisting of a magnetic carrier and a non-magnetic toner. However, in the case of using such a two-component developer, a concentration sensor and other members are required, failing to miniaturize an electrophotographic printer satisfactorily. Accordingly, a one-component developer consisting of a magnetic toner, or a magnetic developer consisting of a magnetic toner and a magnetic carrier is mostly used for the electrophotographic printer.
With the above magnetic developer, the electrophotographic printer can be miniaturized to some extent, but there is a limit in the conventional electrophotographic printer. Since there remain some toner on the photosensitive drum even after transferring a developed image to a recording medium, the conventional electrophotographic printer usually has a cleaning means for the removal of remaining toner, thereby needing more space in the vicinity of the photosensitive drum to place the cleaning means. This has been one of the causes that prevent conventional printers from being greatly miniaturized. Further, since the conventional electrophotographic printer has a heat-fixing means comprising a heat roll containing a heat source and a pressure roll for pressing the recording paper to the heat roll, and since these rolls are provided with paper-separating fingers and other accessories, it is impossible to reduce the height of the roll pair of the heat-fixing means drastically. Accordingly, it has been impossible to make the conventional electrophotographic printer have an extremely reduced thickness.
In the meantime, demands for a portable (hand-carrying) electrophotographic printer as well as for a stationary one have greatly increased recently. Although such a portable electrophotographic printer has already been commercialized for a type of using heat-sensitive papers, the information or image recorded on the heat-sensitive papers will disappear as the time goes. Accordingly, for the purpose of printing information which should be kept for a long period of time, the heat-sensitive paper type electrophotographic printer is not suitable.